This invention relates generally to methods and apparatus for medical treatment and more particularly to methods, devices and systems for administering intra-aortic balloon counterpulsation concurrently with the use of a heat exchange catheter for inducing and maintaining hypothermia in at least a portion of the patient""s body (e.g., cardiac hypothermia, cardiac and cerebral hypothermia, etc.)
A. Intra-Aortic Balloon Pump (IABP) Counterpulsation
An intra-aortic balloon pump (IABP) is a device that may be used to a) increase myocardial blood flow in patients whose cardiac output is compromised due to heart failure or cardiac insufficiency and b) decreases the heart""s workload, through a process called counterpulsation.
During each cardiac cycle, the human heart expels oxygenated blood into the aorta as its left ventricle contracts (i.e., during systole) and, thereafter, receives a backflow of arterial blood into the coronary arteries as its left ventricle relaxes (i.e., during diastole). The systolic pumping of blood into the aorta requires the heart muscle to overcome the static pressure of blood that is already in the aorta. A healthy heart is typically able to perform both of these functions effectively. However, a weakened or failing heart may be unable to perform the work required to fully overcome the static pressure of blood already in the aorta, thereby resulting in less ejection of oxygenated blood into the aorta during systole and less backflow of oxygenated blood into the coronary arteries during diastole.
Intra-aortic balloon counterpulsation is a technique which causes more arterial blood to enter the coronary arteries (and thus more blood flow to the heart muscle) during diastole (less flow work) and decreases the amount of work that the heart must perform during systole (less pressure work). By increasing coronary blood flow, the myocardium receives more oxygen, thereby allowing the heart to pump more effectively and increasing the cardiac output that occurs with each heartbeat (i.e., the xe2x80x9cstroke volumexe2x80x9d).
The IABP comprises a) a balloon catheter that is percutaneously insertable into the patient""s aorta and b) a control console that is attached to the balloon catheter. A computer or controller within the control console receives the patient""s electrocardiogram (ECG). In response to the ECG signal, the controller causes the intra-aortic balloon to be inflated during diastole (when the heart muscle relaxed) resulting in increased back pressure within the aorta and increased blood flow into the coronary arteries, and deflated during early systole (during a phase known as xe2x80x9cisometric contractionxe2x80x9d) resulting in a reduction of intra-aortic pressure against which the heart must pump. In this way, the IABP improves blood flow to the heart muscle and reduces the workload of the heart muscle. Additionally, IABP counterpulsation has been demonstrated to improve peripheral or systemic arterial perfusion. Although the mechanism by which IABP counterpulsation improves peripheral or systemic profusion is not well understood, it is believed that inflation of the intra-aortic balloon during diastole serves to facilitate peripheral runoff (sometimes referred to as the intrinsic xe2x80x9cWindkesselxe2x80x9d effect) which then augments peripheral perfusion.
Preferably, the gas used to inflate the balloon is either carbon dioxide (which has fewer consequences in the rare event of a balloon bursting) or helium (which has the fastest ability to travel or diffuse).
B. The Effects of Hypothermia on Cardiac Function
Mild hypothermia has been shown to both increase the contractility of the heart muscle and to reduce its metabolic requirements. Indeed, if the hypothermia is systemic, the metabolic demands of the entire body are generally reduced, so that the demands placed on the heart may be reduced. Additionally, when the patient""s body temperature is reduced and maintained 1xc2x0 C. or more below normothermic (e.g., less than 36xc2x0 C. in most individuals), such that the output of the heart increases, the condition and function of the heart muscle may improve significantly due to the combined effects of increased bloodflow to the heart, a temporarily decreased metabolic need and decreased metabolic waste products.
One method for inducing hypothermia of the heart or entire body is through the use of a heat exchange catheter that is inserted into a blood vessel and used to cool blood flowing through that blood vessel. This method in general is described in U.S. Pat. No. 6,110,168 to Ginsburg, which is expressly incorporated herein by reference. Various heat exchange catheters useable for achieving the endovascular cooling are described in U.S. Pat. No. 5,486,208 (Ginsburg), PCT International Publication WO 00/10494 (Machold et al.), U.S. Pat. No. 6,264,679 (Keller et al.), U.S. patent application Ser. No. 09/1777,612, all of which are expressly incorporated herein by reference. Other endovascular cooling catheters may be employed to practice this patented method, for example U.S. Pat. No. 3,425,484 (Dato), U.S. Pat. No. 5,957,963 (Dobak III) and U.S. Pat. No. 6,126,684 (Gobin, et al.), provided that they are able to provide adequate hypothermia to the diseased heart.
The potential for shivering is present whenever a patient is cooled below that patients shivering threshold, which in humans is generally about 35.5xc2x0 C. When inducing hypothermia below the shivering threshold, it is very important to avoid or limit the shivering response. The avoidance or limiting of the shivering response may be particularly important in patients who suffer from compromised cardiac function and/or metabolic irregularities. An anti-shivering treatment may be administered to prevent or deter shivering. Examples of effective anti-shivering treatments are described in U.S. Pat. No. 6,231,594 (Dae et al.).
The present invention provides a catheter device that is insertable into the aorta of a human or veterinary patient. Such catheter device comprises a) a balloon that is useable for performing intra-aortic counterpulsation and b) a heat exchanger for exchanging heat with the patient""s flowing blood so as to induce hypothermia of all or a portion of the patient""s body.
Further in accordance with the invention, the catheter device of the foregoing character may be used in combination with driving and control apparatus connected to the catheter for a) causing and controlling the inflation/deflation of the intra-aortic balloon and b) cool or warming the heat exchanger to bring about and maintain the desired hypothermia of all or a portion of the patient""s body. The driving and control apparatus may be positioned extracorporeally and may be housed in one or more consoles that are positioned near the patent""s bed. Preferably, at least the patient""s heart (and in some cases the brain, other portions of the body or the entire body) will be maintained at a temperature 1xc2x0 C. or more below normothermic (e.g., less than 36xc2x0 C. in most humans).
Still further in accordance with the invention, the heat exchanger of the catheter device may comprise less than the entire length of the catheter.
Still further in accordance with the invention, the heat exchanger of the catheter may comprise or be associated with one or more flow-disrupting surface(s) which increase the effective heat exchange surface area and/or alter or disrupt the laminarity of blood flow adjacent to the heat exchanger in a manner that causes some turn over of blood within heat exchange proximity to the heat exchanger and a resultant increase in the efficiency of the heat exchange process.
Still further in accordance with the invention, the heat exchanger of the catheter may be of a flowing fluid type, wherein a fluidic heat exchange medium (e.g., saline solution) is circulated through the catheter and through the heat exchanger. In some embodiments, such flowing fluid type heat exchanger may comprise a flexible structure (e.g., a balloon) which expands or become taut when the heat exchange fluid is circulated therethrough. In some of these embodiments, the heat exchange balloon may be multi-lobed and/or may be curved or twisted (e.g., helical) in configuration. Also, in some embodiments which utilize the flowing fluid type heat exchanger, a wall or surface which separates the patient""s flowing blood from the heat exchange medium being circulated through the heat exchanger may comprise a metal to provide for provide for improved heat transmission between the blood and the heat exchange medium.
Still further in accordance with the invention, in some embodiments the heat exchanger and the counterpulsation balloon may comprise one in the same structure. In this regard, the counterpulsation balloon may be inflated and deflated with a cold gas such that the counterpulsation balloon itself serves as a heat exchanger (in addition to performing its counterpulsation function). Alternatively, a channel or space for recirculation of heat exchange medium (e.g., cooled saline solution) may be formed on or in a wall or portion of the counterpulsation balloon such that heat exchange medium is circulated therethrough as the counterpulsation balloon undergoes repeated inflation and deflation.
Still further in accordance with the invention, in some embodiments, the heat exchanger may be located more distally on the catheter than the counterpulsation balloon, such that when the catheter Is advanced in retrograde fashion into the patient""s aorta to a position where the counterpulsation balloon is properly positioned to perform its counterpulsation function (e.g., within the thoracic aorta), the heat exchanger will be positioned superior to the counterpulsation balloon (e.g., within the aorta between the heart and the counterpulsation balloon).
Still further in accordance with the invention, in some embodiments, the heat exchanger may be located more proximally on the catheter than the counterpulsation balloon, such that when the catheter is advanced in retrograde fashion into the patient""s aorta to a position where the counterpulsation balloon is properly positioned to perform its counterpulsation function (e.g., within the thoracic aorta), the heat exchanger will be located inferior to the counterpulsation balloon (e.g., within the aorta between the counterpulsation balloon and the iliac bifurcation.
Still further in accordance with the invention, the method may be carried out using separate intra-aortic balloon counterpulsation catheter and heat exchange catheters. In such two-catheter embodiments of the method, the heat exchange catheter is separate from the intra-aortic balloon counterpulsation catheter and thus need not necessarily be positioned in the aorta along with the intra-aortic balloon counterpulsation catheter. Rather, the separate heat exchange catheter may be positioned in any suitable blood vessel (vein or artery) to effect cooling of the desired portion of the patient""s body and/or the entire patient""s body. Examples of separate heat exchange catheters and related control systems are described in U.S. Pat. No. 5,486,208 (Ginsburg), U.S. Pat. No. 6,264,679 (Keller et al.), U.S. Pat. No. 3,425,484 (Dato), U.S. Pat. No. 5,957,963 (Dobak III) U.S. Pat. No. 6,126,684 (Gobin, et al.), U.S. Pat. No. 6,264,679 (Keller et al.) and U.S. Pat. No. 5,531,776 (Ward et al.), as well as in PCT International Publication WO 00/10494 (Radiant Medical, Inc.) and copending U.S. patent application Ser. No. 09/777,612, the entireties of which are expressly incorporated herein by reference.
Still further in accordance with the invention, the method may further comprise the step of administering to the patient an anti-shivering treatment such as those described in U.S. Pat. No. 6,231,594 (Dae et al.), the entirety of which is expressly incorporated herein by reference.
Still further aspects and elements of the present invention will become apparent to those skilled in the art upon reading and considering the detailed descriptions of examples set forth herebelow and in the accompanying drawings.